(19)
(11) EP 0 503 878 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
28.07.1993 Bulletin 1993/30

(43) Date of publication A2:
16.09.1992 Bulletin 1992/38

(21) Application number: 92302000.2

(22) Date of filing: 09.03.1992
(51) International Patent Classification (IPC)5: G03G 15/01, G03G 15/09, G03G 13/01
(84) Designated Contracting States:
DE FR GB

(30) Priority: 11.03.1991 US 667921

(71) Applicant: XEROX CORPORATION
Rochester New York 14644 (US)

(72) Inventor:
  • Hogestyn, Larry G.
    Ontario, New York 14519 (US)

(74) Representative: Johnson, Reginald George et al
Rank Xerox Ltd Patent Department Parkway
Marlow Buckinghamshire SL7 1YL
Marlow Buckinghamshire SL7 1YL (GB)


(56) References cited: : 
   
       


    (54) Development apparatus


    (57) An electrophotographic printing machine in which an electrostatic latent image is recorded on a photoconductive surface (10). One portion of the latent image is a discharged area with the other portion of the latent image being a charged area. The discharged image area is developed with toner particles of a first colour and polarity by a first developer unit (32). No greater than 2% by volume of these toner particles have a diameter greater than about 20 microns. The first developer unit (32) generates a weak magnetic field in the development zone and a strong magnetic field at the entrance and exit of the development zone. A second developer unit (34) develops the charged image area with toner of a second colour and polarity. The colours of the toners are different from one another.






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